Sensitized photographic silver halide emulsions



United States Patent Ofiice 3,179,5Zh Patented Apr. 20, 1965 is claims. (Ci. as-ien This invention relates to photographic materials and particularly to light-sensitive silver halide emulsion having improved sensitivity.

In the preparation of a light-sensitive silver halide photographic emulsion, various methods have been known as so-called chemical sensitization to increase its sensitivity.

For example, it is well-known to increase the sensitivity of photographic emulsion by addition of sulfur compounds such as allylthiourea, sodium thiosulfate, etc., which contain labile sulfur atoms and capable of reacting with silver salts to form silver sulfide (compounds of these types are also naturally present in gelatin), or with reducing agents such as stannous chloride and hydrazine derivatives, or with salts of gold such as aurous thiocyanate, or with combinations of two or more of the aforementioned compounds generally known as chemical sensitizeis. (See P. Glafkides, Chimie Photographique, Paul Montel, Paris (1957), p. 297 and p. 301.)

Such chemical sensitizers are believed to form, on the surface of the silver halide, minute amounts of silver sultide or of silver or of gold, and these processes are capable of increasing the sensitivity of developing-out emulsions by very large factors.

The process of chemical sensitization, however, generally presents some increase of fog, and moreover reaches a definite limit beyond which further addition of sensitizer, or of further ripening with the sensitizer present, merely increases the fog of the photographic emulsion with constant or decreasing sensitivity.

It is also well-known in the art that there is, at the present time, a practical limit to the advantages which can be obtained by the addition of such compounds without presenting deleterious effects such as instability on tropical aging.

We have now found a novel and effective chemical sensitizing method, which does not belong to any of the above-mentioned chemical sensitizing methods, but increases the sensitivity of the silver halide photographic emulsion without presenting any increase of fog, and at the same time even improves the stability of the said emulsion on tropical aging. Moreover the novel sensitizers of our invention may be used together with labile sulfur compounds, reducing agents and/ or gold compounds, thereby we can further increase the sensitivity of the emulsion.

However, the novel sensitizers of our invention can be used to sensitize photographic silver halide emulsions containing no other sensitizers.

According to our invention, we have found that the sensitivity of an ordinary photographic silver halide emulsion can be increased by incorporating therein at least one organo-mercury compound having the following general formula:

wherein R indicates an alkyl group, X is a member selected from a class consisting of hydroxyl group and organic and inorganic acid radicals, and n is an integer of froml to 2, corresponding to the valency of X, and ripening the said emulsion.

Therefore, one object of our invention is to increase the sensitivity of the light-sensitive photographic emulsion without increasing fog.

Another object is to provide photographic emulsions containing the novel sensitizers. Other objects will become apparent from the following description of our invention. i

The following compounds may be used according to our invention: methylmercuri chloride, methylmercuri iodide, bis(methylmercuri) sulfate, ethylrnercuri chloride, ethylmercuri hydroxide, bis(ethylmercuri) phosphate, eth lymercuri acetate, n-butylrnercuri cyanate, isopropylmercuri bromide, n-octylmercuri chloride, n-dodecylmercuri iodide, ethylmercuri p-toluenesulfonate, etc.

Inorganic and organic mercury compounds have been known hitherto as additives having stabilizing action, which, when added in minute quantity to a finished silver halide photographic emulsion, reduce its fog without appreciably affecting the sensitivity of the sensitive material, and further maintain the sensitivity and fog of the said silver halide emulsion at or close to initial optimum values under keeping conditions of high temperature and high humidity. (See e.g. US. Patents 2,728,663--2,728,667, 2,732,562, 2,751,299, etc.)

The organo-mercury compounds represented by the above general formula and used according to the present invention, however, have never been described to be used as additives for photographic emulsion in any patents or literatures. Furthermore, according to the present invention, the organo-mercury compounds are added to the photographic emulsion at any stage of preparing the said emulsion, particularly before and during chemical ripening, while the organo-mercury compounds disclosed in the above-rnentioned patents are added to the finished photographic emulsion before coating,to act as antifoggants and stabilizers.

The organo-mercury compounds of our invention are dissolved in water or other solvents which have no harmful effects upon the emulsion, and generally solvents which are miscible with Water are to be preferred. In a preferred embodiment, the sensitizer can be dissolved in solvents such as water, methanol, etc., and added to the emulsion in this form.

The particular quantity of the organo-mercury compound used in a given emulsion can vary, depending upon the effect desired, degree of ripening, silver content of the emulsion, etc. The amount used is also dependent upon the partcular stage at which the sensitizer is added during the preparation of the emulsion. Although we found that from about 0.05 mg. to about 5.0 mg. of the sensitizer per mole of silver halide is quite adequate to accomplish the desired sensitization of many of the comrnon photographic silver halide emulsions, these limits are merely illustrative.

As supports on which the photographic emulsion prepared according to our present invention is to be coated, ordinary supports for photographic emulsion such as glass, cellulose triacetate film base, polyethylene terephthalateiilm base, harytaged paper, etc. are used.

In addition, the sensitized emulsions of our invention can be used in the preparation of color photographs. This may be accomplished either by using photographic emulsions containing color-forming compounds or coll.- plers which are well-known in the art, or by the use of photographic emulsions which are developed in color developers containing colonforrning compounds or conpiers also well-known in the art.

The following examples will further illustrate the invention, but it is to be understood that it is not limited thereto.

. N-methyl-p-aminophenol sulfate N-methyl-p-aminophenol sulfate sion is ripened at 50 C. for 60 minutes under stirring.

Thereafter, 30 mg. of 1,1-diethyl-2,2'-cyanine iodide,

0.45 g. of chrome alum and 0.12 g. of saponin are added to the emulsion and the mixture is coated on cellulose triacetate film base and dried. This film is exposed on an-intensity scale sensitometer to 5400 K. illumination for second and developed at 20 C. in a developing solution of the following composition:

G. 2.0 Hydroquinone 5.0 Sodium sulfite (anhydrous) 100.0 Borax 2.0 Water to 1.0 litre.

Fresh Test After incubation (1 week at 40 0.)

Relative Sensitivity Relative Sensitivity Gnm- Fog Gam- Fog

Emulsion with Hg Compound Emulsion without Hg compound Example 2 A gelatino-silver chlorobromide emulsion is prepared and ripened for 30 minutes at 52 C., with 120 mg. of sodium thiosulfate per mole of silver halide. This emul sion is divided into three equal portions and one portion is further ripened for 30 minutes at 52 C. with 10 ml. of a 0.001% aqueous solution of bis(ethylmercuri) phosphate per mole of silver halide.

The second portion is further ripened for 30 minutes at 52 C. with 10 ml. of a 0.001% aqueous solution of n-hexylmercuri acetate per mole of silver halide, while the third portion is ripened as a control with 10 ml. of distilled water per mole of silver halide, for 30 minutes at 52 C., and all three portions are coated on cellulose triacetate film base and dried to produce a thin emulsion layer (about 10 microns).

The resulting coatings are exposed on an intensity scale sensitometer to 2,666 K. illumination for second and developed for 4 minutes at 20 C. in a developer of the following composition:

G. 0.3 Potassium metabisulfite 1.4 Sodium sulfite (anhydrous) 38.0 Hydroquinone 6.0 Sodium carbonate (monohydrate) 22.5 Citric acid 0.7 Potassium bromide 0.9 Water to 1.0 litre.

Sensitometric measurements show the increase of sensitivity and gamma:

Relative sonsi- Gamma Fog tivity sensitized with bis(ethylmercu ri) phoshate 121 2. 00 0. 04 sensitized with n-liexylmereuri acetatm. 109 2. 88 0.05 Control 2. 52 0. 05

Example 3 To a washed full ammoniacal gelatino-silver iodobromide photographic emulsion containing 1 mole of silver halide, in which the silver halide consists of 2.2 mole percent of AgI and 97.8 mole percent of AgBr, there is added 1.2 cc. of a 0.01% methanolic solution of triethylthiourea, 5.0 cc. of a 0.01% aqueous solution of HAuCl .4H O admixed With 4.0 cc. of a 0.1 N aqueous solution of NH SCN, and thereafter the emulsion is ripened for 40 minutes at 50 C.

To one-half of the ripened emulsion is added 8 cc. of a 0.001% m-ethanolic solution of bis(methylmercuri)- adipate, and thereatfer the emulsion is further ripened for 15 minutes at 50 C.

The emulsion thus obtained is added under stirring at 35 C., 0.3 g. of 4-hydroxy-6 methyl-1,3,3a,7-tetrazaindene, 0.2 g. of chrome alum and 0.2 g. of saponin, and then the mixture is coated on cellulose triacetate film and dried in the usual manner to produce a thin emulsion layer (12 microns).

'The other half of the emulsion is handled in like man ner except that the solution of the mercury compound is omitted.

These two films are exposed on an intensity scale sensitometer to 5400 K. illumination and developed for 4 minutes at 20 C. in a solution of the following composition:

Example 4 A solution of 26 g. of potassium chloride, 7 g. of potassium bromide and 8 g. of gelatin in 230 ml. of dis tilled water is maintained at 45 C., whereto a solution of 50 g. silver nitrate in 920 cc. distilled water is added in 15 minutes under stirring, the temperature being kept at 55 C. After the adding of 100 g. of gelatin, the emulsion is further stirred for 15 minutes, then chilled With ice, noodled and washed with running water at about 10 C., until the conductivity of the emulsion is 1,500 micromhos, and thereafter the emulsion is remelted.

To one-half of the emulsion is added 1.2 g. of active gelatin, 2.5 cc. of a 0.01% aqueous solution of HAuCL; 4H 0 1.3 cc. of' a 0.1 N aqueous solution of KSCN and 2.0 cc. of a 0.001% methanolic solution of ethylmercuri ptoluenesulfonate, and thereafter the emulsion is ripened for 4-0 minutes at 55 C.

The emulsion thus obtained is added under stirirng at 35 C., 10 cc. of a 0.05% methanolic solution of 3- a1lyl-3-ethyl-5 (2- 1-ethyl-4 quinolinidene ethylidene) ',6-dimethyl 4 oxothiazolino oxacyanin iodide and 200 cc. of a 5% alkaline solution of N-octadecyl-l-hydroxy-4-sulfo-2-naphthamide, and then the mixture is coated on cellulose triacetate film which has previously been given a subcoating, and dried to produce a thin emulsion layer.

Sensitometric measurements show the speed of the film thus coated and dried to be 1.22 times that of the film prepared from the same ingredients and in the same manner with the single exception that the emulsion used is ripened without ethylmercuri p-toluenesulfonate.

What we claim is:

1. A photographic silver halide emulsion sensitized by at least one mercury compound having the formula (R-I-Ig) X wherein R represents an alkyl group, X represents a member selected from the class consisting of hydroxyl group and organic and inorganic acid radicals, and n represents an integer of from 1 to 2, corresponding to the valency of X.

2. A photographic silver halide emulsion according to claim 1 wherein the mercury compound is present in a quantity of ODS-5.0 mg. per mole of silver halide.

3. A photographic silver halide emulsion according to claim 1, wherein the alkyl group contains up to 12 carbon atoms.

4. A photographic silver halide emulsion sensitized by at least one mercury compound having the formula (R-Hg) X wherein R is an alkyl group having up to 12 carbon atoms, X is a member selected from the class consisting of hydroxyl group and organic and inorganic acid radical, and n is an integer of from 1 to 2 corresponding to the valency of X wherein the mercury compound is present in a quantity of ODS-5.0 mg. per mole of silver halide.

5. A photographic silver halide emulsion according to claim 4, wherein the mercury compound is a methylmercuri chloride.

6. A photographic silver halide emulsion according to claim 4, wherein the mercury compound is bis-(ethylmercuri) phosphate.

7. A photographic silver halide emulsion according to claim 4, wherein the mercury compound is bis-(methylmercuri) adipate.

8. A photographic silver halide emulsion according to claim 4, wherein the mercury compound is ethylmercuri p-toluene sulfonate.

9. A photographic silver halide emulsion sensitized by at least one mercury compound in the ratio of 0.05-5.0 mg. per 1 mole of silver halide having the formula (R-Hg) X wherein R is an alkyl group having up to 12 carbon atoms, X is a member selected from the class consisting of hydroxyl group and organic and inorganic acid radicals, and n is an integer of from 11 to 2, corresponding to the valency of X, and containing a labile sulfur compound.

10. A photographic silver halide emulsion sensitized by at least one mercury compound in the ratio of 0.05- 5.0 mg. per 1 mole of silver halide having the formula (RHg) X wherein R is an alkyl group having up to 12 carbon atoms, X is a member selected from the class consisting of hydroxyl group and organic and inorganic acid radicals, and n is an integer of from 1 to 2, corresponding to the valency of X, said emulsion also containing a labile sulfur compound and a gold compound.

References Cited by the Examiner UNITED STATES PATENTS 2,540,086 2/51 Baldsiefen et a1. 96--l08 2,728,665 12/55 Leubner et al. 96109 2,728,666 12/55 Carroll 96-l07 3,128,184 4/64 Lowe et a1. 96-408 NORMAN G. TORCHIN, Primary Examiner. 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION SENSITIZED BY AT LEAST ONE MERCURY COMPOUND HAVING THE FORMULA (R-HG)NX WHEREIN R REPRESENTS AN ALKYL GROUP, X REPRESENTS A MEMBER SELECTED FROM THE CLASS CONSISTING OF HYDROXYL GROUP AND ORGANIC AND INORGANIC ACID RADICALS, AND N REPRESENTS AN INTEGER OF FROM 1 TO 2, CORRESPONDING TO THE VALENCY OF X. 